U.S. patent number 4,779,805 [Application Number 06/841,022] was granted by the patent office on 1988-10-25 for electrostatic sprayhead assembly.
This patent grant is currently assigned to Imperial Chemical Industries PLC. Invention is credited to Arend L. Grocott, Alastair J. Jackson.
United States Patent |
4,779,805 |
Jackson , et al. |
October 25, 1988 |
Electrostatic sprayhead assembly
Abstract
An electrostatic spray head is charged with high voltage from a
high voltage source. As a liquid to be sprayed is supplied to the
spray head, the liquid is atomized predominately due to the high
voltage. The spray head is located within or closely adjacent to a
gas stream flowing along a path which extends in the spraying
direction, so that at least some of the atomized liquid becomes
entrained in the gas stream. The gas stream has a lower velocity
region and a high velocity region, of which the lower velocity
region is transversally closer to the spray head.
Inventors: |
Jackson; Alastair J.
(Hampshire, GB), Grocott; Arend L. (Hampshire,
GB) |
Assignee: |
Imperial Chemical Industries
PLC (London, GB2)
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Family
ID: |
10533569 |
Appl.
No.: |
06/841,022 |
Filed: |
March 17, 1986 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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534116 |
Sep 20, 1983 |
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Foreign Application Priority Data
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Oct 13, 1982 [GB] |
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8229219 |
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Current U.S.
Class: |
239/704;
239/296 |
Current CPC
Class: |
A01M
7/0089 (20130101); B05B 5/03 (20130101); B05B
9/06 (20130101); B05B 7/067 (20130101); F02B
1/04 (20130101) |
Current International
Class: |
A01M
7/00 (20060101); B05B 5/03 (20060101); B05B
9/04 (20060101); B05B 5/025 (20060101); B05B
9/06 (20060101); B05B 7/06 (20060101); B05B
7/02 (20060101); F02B 1/00 (20060101); F02B
1/04 (20060101); B05B 005/02 () |
Field of
Search: |
;239/690,704,706,77,290,291,296 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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901969 |
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Jul 1962 |
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GB |
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978763 |
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Dec 1964 |
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GB |
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1107060 |
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Mar 1968 |
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GB |
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1143839 |
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Feb 1969 |
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GB |
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1307878 |
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Feb 1973 |
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GB |
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1376637 |
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Dec 1974 |
|
GB |
|
1569707 |
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Jun 1980 |
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GB |
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2052627 |
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Jan 1981 |
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GB |
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Primary Examiner: Kashnikow; Andres
Assistant Examiner: Forman; Michael J.
Attorney, Agent or Firm: Cushman, Darby & Cushman
Parent Case Text
This is a continuation-in-part of application Ser. No. 534,116,
filed Sept. 20, 1983 which was abandoned.
Claims
We claim:
1. An electrostatic sprayhead assembly, comprising:
an electrostatic spray head; means connected to said spray head for
supplying liquid to said spray head; a source of high voltage;
means connecting said spray head with said source of high voltage
for charging said spray head to a high voltage as liquid is
supplied to said spray head, thereby coacting with said spray head
for atomizing that liquid predominantly by means of said high
voltage, as such liquid issues from said sprayhead;
means for forming a gas stream having a velocity along a path in a
spraying direction;
said spray head being located within or closely adjacent to said
gas stream path such that at least some of the atomized liquid
issued from said sprayhead in use become entrained in said gas
stream for transport in said direction therewith;
said gas stream forming means including:
means for forming a first, lower velocity gas stream region located
closer to said spray head in a direction transversally of said
path, this means having an inlet and an outlet;
means for forming a second, high velocity gas stream region located
further from said sprayhead in a direction transversally of said
path, with said first, lower velocity gas stream region intervening
between said sprayhead and said second higher velocity gas stream
region, this means also having an inlet and an outlet; and
an outlet of said sprayhead being disposed at or near the same
location in said spraying direction as said outlet of said means
for forming said first, lower velocity gas stream region.
2. The electrostatic sprayhead of claim 1, wherein:
said means for forming a second, high velocity gas stream region
comprises means defining an annular channel at least generally
circumferentially surrounding both said electrostatic sprayhead and
said means for forming said first, lower velocity gas stream
region.
3. The electrostatic sprayhead of claim 2, wherein:
said means for forming said first, lower velocity gas stream region
comprises means defining another annular channel at least generally
circumferentially surrounding said electrostatic sprayhead.
4. The electrostatic sprayhead assembly of claim 2, comprising:
a high voltage generator disposed in proximity to said sprayhead
and in position to be at least partially circumferentially
surrounded, in use, by said gas stream for providing said source of
high voltage.
5. The electrostatic sprayhead assembly of claim 4, wherein:
said means for forming said first, lower velocity gas stream region
comprises means defining another annular channel at least generally
circumferentially surrounding said electrostatic sprayhead.
6. The electrostatic sprayhead assembly of claim 5, wherein:
said sprayhead, said means for forming said first, lower velocity
gas stream region, and said means for forming said second, higher
velocity gas stream region are mutually substantially coaxial with
one another.
7. The electrostatic sprayhead of claim 1, wherein:
said inlet of said means for forming a first, lower velocity gas
stream region is constructed and arranged for communication to a
lower pressure source of gas;
said inlet of said means for forming a second, higher velocity gas
stream region is constructed and arranged to be connected to a
higher pressure source of gas;
said means for forming a gas stream being constructed and arranged
to place said outlet of said second, high velocity gas stream
region, in use, in such effective contact with said outlet of said
first, lower velocity gas stream region as to cause gas to be drawn
into said means for forming said first, lower velocity and stream
region through said inlet thereof from said lower pressure source
of gas for providing said first, lower velocity gas stream
region.
8. The electrostatic sprayhead of claim 7, wherein:
said inlet of said means for forming a first, lower velocity gas
stream region comprises means for communicating said means for
forming said first lower velocity gas stream region to atmospheric
air as said lower pressure source of gas; and
said inlet of said means for forming a second, higher velocity gas
stream region comprises a source of pressurized air and means for
communicating said means for forming said second, higher velocity
gas stream region to said source of pressurized air as said higher
pressure source of gas.
9. The electrostatic sprayhead assembly of claim 1, further
including:
a high voltage generator disposed in proximity to said sprayhead
and in position to be at least partially circumferentially
surrounded, in use, by said gas stream for providing said source of
high voltage.
10. The electrostatic sprayhead assembly of claim 9, wherein:
said means for forming said first, lower velocity gas stream region
comprises means defining another annular channel at least generally
circumferentially surrounding said electrostatic sprayhead.
11. The electrostatic sprayhead assembly of claim 10, wherein:
said sprayhead, said high voltage generator, said means for forming
said first, lower velocity gas stream region, and said means for
forming said second, higher velocity gas stream region are mutually
substantially coaxial with one another.
12. The electrostatic sprayhead assembly of claim 11, wherein:
said high voltage generator is disposed axially behind said
sprayhead.
13. The electrostatic sprayhead assembly of claim 12, wherein:
said inlet of said means for forming a first, lower velocity gas
stream region comprises a source of lower pressure gas and means
for communicating said means for forming said first lower velocity
gas stream region to said lower pressure source of gas;
said inlet of said means for forming a second, higher velocity gas
stream region comprises a source of pressurized air and means for
communicating said means for forming said second, higher velocity
gas stream region to said higher pressure source of gas;
said means for forming a gas stream being constructed and arranged
to place said outlet of said second, higher velocity gas stream
region, in use, in such effective contact with said outlet of said
first, lower velocity gas stream region as to cause gas to be drawn
into said means for forming said first, lower velocity gas stream
region through said inlet thereof from said lower pressure source
of gas for providing said first, lower velocity gas stream
region.
14. The electrostatic sprayhead assembly of claim 13, wherein:
said inlet of said means for forming a first, lower velocity gas
stream region comprises means for communicating said means for
forming said first lower velocity gas stream region to atmospheric
air as said lower pressure source of gas; and
said inlet of said means for forming a second, higher velocity gas
stream region is comprises a source of pressurized air and means
for communicating said means for forming said second, higher
velocity gas stream region to said source of pressurized air as
said higher pressure source of gas.
Description
This invention relates to electrostatic sprayhead assemblies for
use with spraying devices of the type employing a blast of gas to
assist transport of the liquid being sprayed.
Such devices include mistblowers which have been known for many
years as a convenient and effective way of applying pesticides to
crops. They may be either portable or tractor mounted. A portable
machine will, for example, typically comprise an engine (e.g. a
two-stroke petrol engine) driving a fan which provides a strong
current of air to a spray lance carried in the operator's hand. A
liquid spray reservoir, carried with the engine or fan on the
operator's back, feeds liquid pesticides to a nozzle within the
spray lance. The force of the air current passing through the
nozzle spray lance shatters the liquid emerging from the nozzle
into fine droplets, which are entrained in the current of air. They
pass out through the head of the lance, and are carried by the
current of air onto and into the crop being sprayed.
Mistblowers have the advantage that they produce much better
penetration of pesticide sprays into crops than is obtained with
devices which do not have air assistance. They can also be used to
spray objects above the level of the sprayer, e.g. fruit trees.
However, they do have certain disadvantages. Thus, the strong
current of air they produce can carry some pesticide droplets right
through the crop. Such droplets may then drift for considerable
distances, and become a potential ecological hazard. This problem
is increased by the method of formation of the droplets. Droplets
produced by a fluid shear mechanism tend to be quite irregular in
size. Many droplets are thus produced below the ideal size, and
these small droplets are particularly prone to drift for long
distances.
Electronic spraying processes are known which produce a spray of
charged droplets. Such spraying processes have numerous advantages,
including in particular that charged droplets are positively
attracted to target plants by electrostatic forces, and coat them
evenly. Both upper and lower sides of leaves can be coated.
However, because of the attractive electrostatic forces, the
charged spray particles find it difficult to penetrate far into a
crop canopy.
Electrostatic spraying processes are of two main types. In the
first type the spray droplets are formed by air or liquid pressure
prior to charging, such charging typically being performed with
corona discharge electrodes. Sprays formed in this way are
relatively insensitive to ambient conditions including air flow,
and indeed often utilise air-shear for droplet formation.
In the second type, atomisation of liquid into spray droplets takes
place under the influence of an electric charge on the sprayhead,
atomisation being caused predominantly by electrical forces. Such
processes produce a fine uniform droplet size with light charging
efficiency but are sensitive to ambient conditions such as air-flow
which can interfere with spray formation.
We have now found surprisingly that it is possible to obtain
satisfactory spray formation with processes of the second type when
the sprayhead is located directly within the air stream produced by
an air blower. In this way the advantages of efficient spray
formation can be combined with the benefit of air assistance to
give good crop penetration and efficient crop coverage with reduced
spray drift.
Accordingly the present invention provides a sprayhead assembly
comprising an electrostatic sprayhead chargeable to a high voltage
and adapted to atomise liquid to be sprayed at least predominantly
by means of the high voltage, the sprayhead being connectable to
sources of high voltage and liquid; and a means for forming a
stream of gas, in which the sprayhead is located within or closely
adjacent to the stream of gas in use whereby atomised liquid formed
by the sprayhead is at least partly entrained in the stream of
gas.
The means for forming the stream of gas is conveniently a channel
connectable to a source of gas which is generated directly or
indirectly by a powered blower.
The electrostatic sprayhead is preferably of the type disclosed in
our UK Pat. No. 1569707 having an earthed field intensifying
electrode adjacent to an electrostatically charged spray
nozzle.
Specific embodiments of the invention will now be described with
reference to the drawings, in which:
FIG. 1 is a partial diagrammatic side view of a sprayhead assembly
according to the invention connected to an air blower.
FIG. 2 is an end view of the apparatus of FIG. 1;
FIG. 3 is a line diagram including a sprayhead assembly similar to
that shown in FIG. 1 and showing the control and supply system
therefor;
FIG. 4 is a more detailed, exploded, axial, sectional view of the
sprayhead forming part of the assembly of FIG. 3;
FIG. 5 is an axial section through another sprayhead assembly
according to the invention showing a part of an air supply
therefore; and
FIG. 6 is a plan of the assembly of FIG. 5.
The drawings are not to scale.
Referring to FIGS. 1 and 2 of the drawings an air blower consisting
of a motor (1) and a fan (2) delivers air to a flexible tube (3)
connected by a detachable coupling (4) to a pipe (5) of diameter
approximately 9 cms forming a channel for a stream of air. The pipe
(5) positions and supports electrostatic sprayhead (6) (approximate
diameter 4 cm) via internal struts (7) within the stream of air
(diagrammatically illustrated by arrow A of FIG. 1) delivered by
the blower.
The electrostatic sprayhead (6) is of the type described in our UK
Pat. No. 1569707 having an earthed field adjusting electrode
surrounding and insulated from a conducting spray nozzle charged to
a potential of about 25 kilovolts.
The sprayhead is provided with a liquid supply via a flexible tube
(not shown) connected to a pump. It is likewise provided with
electrical connections (not shown) to earth and to a source of high
voltage.
Referring to FIG. 3 in an arrangement similar to that of FIGS. 1
and 2 the sprayhead (6) is connected to a high voltage generator
(8) also located in the airstream generated by the blower (2). The
sprayhead is located approximately flush with the exit of pipe (5)
and is supplied with liquid via line (9) from a metering pump (10)
fed from a liquid container (11) and controlled from control box
(12) and control console (13). Pump (10) may be electrically driven
or use engine power or pressurised gas etc. Console (13) also
controls the electrical input to the high voltage generator (8) via
line (14) and control box (12).
Power is supplied to the control box from a battery (15).
Referring to FIG. 4 the sprayhead is seen to comprise a nozzle (20)
of conducting material, shaped to provide an annular edge (21) from
which liquid is atomised by high voltage applied to the nozzle.
Liquid is supplied to the nozzle from inlet (22) via liquid
channels (23, 24 and 25). High voltage is supplied to the nozzle
from generator (8) via lead (26) when the nozzle (20) is screwed
into recess (27) in connecting piece (32) with internally threaded
collar (28).
The nozzle (20 ) is surrounded by a hollow insulating sleeve (29)
in which a ring-shaped field-adjusting electrode (30) is located.
Electrode (30) is connected to earth via lead (31).
In operation (in spraying a crop with pesticide for example) the
sprayhead (6) is supplied with liquid and the appropriate
electrical connections are made, resulting in a spray of highly
charged particles of very uniform size being incorporated into the
stream of air supplied by the blower. The droplets will of course
tend to fan out but the overall effect is for the movement of
particles towards the crop to be reinforced, and the spray
characteristics to be influenced, by the airstream from the
blower.
The apparatus illustrated is especially suitable for mounting on
knap-sack frames and tractors and can be used to spray crops at a
variety of angles.
The air blast materially increases penetration into the crop,
thereby improving pesticide deposition within it. However, there is
a much reduced tendency for droplets to be carried through the
crop, because of the electrostatic force between crop and
particles. In general, charged droplets carried through the crop
are able to overcome the force of the airflow, by this time much
attenuated, and are attracted back onto the crop. Because of the
uniformity of particle size produced by electrostatic atomisation,
drifting problems are much reduced.
Typical operating parameters are as follows:
______________________________________ Air speed (at outlet) 20-25
meters/sec Nozzle to crop distance 2-4 meters Droplet size approx.
30 .mu.m at nozzle voltage approx. 30 kv and liquid flow rate 0.05
ml/sec ______________________________________
Referring to FIGS. 5 and 6 an alternative sprayhead assembly
comprises a nozzle (40) and a generator (41) of the type
illustrated in FIG. 4. Liquid and electrical input are provided via
connections (43) and (44), respectively. The nozzle (40) is mounted
within a pipe (42) which is open at both ends and provides a
channel (49) for a stream of air, as hereinafter described. An
outlet of the nozzle (40) is disposed at or near the same axial
location, i.e. at or near the same location in the spraying
direction, as an outlet end of the pipe (42).
The outlet-end of pipe (42) is surrounded by a second pipe (45)
forming an annular air channel (46) between the two pipes. Channel
(46) is supplied with air under pressure from a pipe (47) via an
elbow union (48). Pipe (47) is connected to an air trunking system
50 carried on a tractor (not shown).
In use, a stream of relatively fast-flowing pressurized air from
the pipe (47) flows through the channel (46), as indicated by the
arrow D. This stream D draws a stream C of relatively slow-moving
atmospheric air into an open inlet (51) of the pipe (42) and past
the nozzle (40). It is found that this arrangement interferes less
with spray formation especially under more marginal conditions
which may arise from faster liquid flow-rates or the use of liquids
which do not atomize so well.
The reason for this can be understood by considering the flow
conditions in an assembly having only a single pressured air-stream
which flows through the channel 49 of FIG. 5. The effect of this
air-stream is to produce a region of low pressure adjacent the
outlet of the nozzle 40. Within this low pressure region there is
considerable turbulence, which disturbs the formation of cones and
ligaments of liquid otherwise produced by the electrostatic
atomization process and leads to contamination of nearby parts of
the assembly. In fact, atomization is largely effected by
air-shearing of the liquid, rather than electrostatic forces, and
there is a wide variation in the size of atomized droplets of
liquid.
With the assembly of FIG. 5, the lower velocity stream C does not
produce a low pressure region adjacent the nozzle outlet and the
electrostatic atomization process is undisturbed. Once the droplets
have been formed and have moved away from the nozzle outlet they
are, however, entrained by the higher velocity stream D, which
carries them towards and into the crop.
In FIG. 5 the outlet of the nozzle is a short distance downstream
of the outlet end of the pipe (42). In alternative embodiments the
nozzle outlet has the same location in the spraying direction as
does the pipe outlet. In further embodiments the nozzle may be a
short distance upstream of the pipe outlet, provided the liquid and
air flow and the electrical parameters are not such as to cause
droplets to be deposited on the inner surface of the pipe 49.
Typical operating parameters are:
______________________________________ Fluid flow rate up to 1
ml/sec Nozzle voltage 20-40 kv Air volume of greater than 2.5 cubic
meters/min pressurised air Air speed of 20-40 meters/sec
pressurised air ______________________________________
Sprayhead assemblies of the present invention may be used singly or
mounted in linear or circular arrays comprising more than one
assembly. Circular arrays may be adapted to spray either in a
radial or an axial direction.
It is also within the scope of the invention for more than one
sprayhead to be located within a given air stream.
Examples of results obtained using a sprayhead assembly of the type
illustrated with reference to FIGS. 1-4 will now be described.
EXAMPLE 1
Bush tomato plants were sprayed to control whitefly using a
pesticide formulation containing cypermethrin. Percentage control
relative to untreated plants are recorded. Comparative results
using a similar sprayhead without air assistance and a conventional
hydraulic nozzle were also obtained.
The sprayhead assembly of the invention was operated as
follows:
______________________________________ Air speed at outlet 20-25
meters/sec Nozzle to crop 2-4 meters distance Droplet size approx.
30 .mu.m. Nozzle voltage approx. 30 kv Flow rate of 0.05 ml/sec
pesticide ______________________________________
The other sprayheads were operated at what were judged to be
optimum conditions.
The results are given in Table I.
TABLE I ______________________________________ % Control against
untreated 1 liter/ha = 15 g active ingredient/ha Electrostatic
Conventional Days after sprayhead no Present 45 g ai/ha, treatment
air assistance invention 400 l/ha
______________________________________ 1 51 98 36 4 76 97 15
______________________________________
The results show the present invention to give by far the greatest
initial knock-down and also the longest persistence in spite of the
conventional treatment being applied at three times the rate per
hectare.
EXAMPLE 2
Trials were performed to indicate optimum air speed. Results are
set out in Tables II and III from which it is seen that better
results are obtained at somewhat lower air speeds than
conventionally used with air blowers.
Comparison of Different Operating Parameters
______________________________________ (i) Crop tomatoes Pest
Whitefly Pesticide cypermethrin Rate 1 liter/ha 15 g ai/ha
______________________________________
TABLE II ______________________________________ % Control Compared
with Untreated: 1 Day After Treatment Air Speed Air Speed 25 m/s at
outlet 50 m/s at outlet ______________________________________ Top
Canopy 90 78 In-Canopy 73 60
______________________________________
______________________________________ (ii) Crop Cucumbers Pest
Whitefly Pesticide cypermethrin Rate 1 liter/ha = 15 g active
ingredient/ha ______________________________________
TABLE III ______________________________________ % Control Compared
with Untreated: 1 Day After Treatment Air Speed Air Speed 25 m/s at
outlet 50 m/s at outlet ______________________________________ Top
Canopy 87 71 In-Canopy 83 65
______________________________________
The results show that an air speed of 25 m/s at the air outlet
gives superior top canopy and in-canopy control to the higher air
speed of 50 m/s at the outlet.
* * * * *